The present invention relates to a network of central processing complexes (CPCs) connected by intersystem channels to a coupling facility, each CPC having data objects used to maintain state information for shared data in the coupling facility storage, and more particularly relates to a mechanism in the coupling facility for dispatching a new message command for execution when such command dispatch is permitted by the link states.
Command dispatching consists of three main actions; first the arrival of a command is detected by the dispatcher function executing on one of the processors in the coupling facility, second the ownership of the command is obtained by this processor to isolate command execution from the dispatcher running concurrently on another processor, and lastly, the error state of each of the links attached to the coupling facility is checked to see if any errors may be present for commands in execution on another coupling facility processor. The last function is essential to the correct implementation of the command quiesce rules defined in the related application U.S. Ser. No. 07/860,330, Command Quiesce Function (D. A. Elko et al.). The error state reporting mechanism for intersystem channels is defined in the related application U.S. Ser. No. 07/860,800, Integrity of Data Objects Used to Maintain State Information for Shared Data at a Local Complex (D. A. Elko et al.), and represents prior ad to the present invention.
A dispatcher function in the coupling facility may be built on the mechanisms defined in U.S. Ser. No. 07/860,800 and the mechanisms in the related application
The main drawback of this approach is the pathlength incurred on each command for the overhead of testing each link individually for the presence of an error across a long-latency path in the hardware. The test requires a sense command to be communicated between the processor and the intersystem channel, and while generally deemed to have adequate performance when a single link is tested, may become quite costly when multiple links are involved. Also, as the number of processors available for the coupling facility grows, so does the overhead of testing for error conditions.